Inverted metamorphic multijunction solar cells for space applications

A multijunction solar cell comprising:

• an upper first solar subcell having a first band gap;
• a second solar subcell adjacent to said upper first solar subcell and having a second band gap;
• a third solar subcell adjacent to said second solar subcell and having a third band gap;
• a fourth solar subcell disposed below said third solar subcell, said fourth subcell having a fourth band gap less than the third band gap of said third solar subcell;
• and
• a fifth solar subcell disposed below said fourth solar subcell and forming a bottom solar subcell of the multijunction solar cell, said fifth solar subcell having a fifth band gap less than the fourth band gap and composed of GaInAs,
• wherein the third solar subcell is composed of a GaAs emitter layer and a GaAs base layer so as to optimize energy conversion efficiency of the solar cell after exposure to radiation a 1 MeV electron equivalent fluence over 5×1014 electrons/cm2 or more, and
• wherein composition of the third solar subcell is designed to increase solar cell efficiency at EOL while disregarding the solar cell efficiency at BOL, such that the solar cell efficiency at the BOL is less than the solar cell efficiency at the BOL that would be achieved if the composition were designed to maximize the solar cell efficiency at the BOL.

A method of manufacturing a solar cell comprising:

• providing a first substrate;
• depositing on the first substrate a first sequence of layers of semiconductor material forming an upper first solar subcell, a second solar subcell, and a third solar subcell;
• depositing on said third solar subcell a first graded interlayer;
• depositing on said first graded interlayer a second sequence of layers of semiconductor material forming a fourth solar subcell, the fourth solar subcell being lattice mismatched to the third solar subcell;
• depositing on said fourth solar subcell a second graded interlayer;
• depositing on said second graded interlayer a third sequence of layers of semiconductor material forming a fifth solar subcell, the fifth solar subcell being lattice mismatched to the fourth solar subcell;
• mounting and bonding a surrogate substrate on top of the third sequence of layers;
• and
• removing the first substrate;
• wherein the first graded interlayer is compositionally graded to lattice matched the third solar subcell on one side and the fourth solar subcell on the other side, and is composed of one or more As, P, N, Sb based III-V compound semiconductors subject to constraints of having an in-plane lattice parameter greater than or equal to that of the third solar subcell and less than or equal to that of the lower fourth solar subcell, and having a band gap energy greater than that of the third solar subcell and the fourth solar subcell;
• wherein the second graded interlayer is compositionally graded to lattice match the fourth solar subcell on one side and the lower fifth solar subcell on the other side, and is composed of any of the As, P, N, Sb based III-V compound semiconductors subject to constraints of having an in-plane lattice parameter greater than or equal to that of the fourth solar subcell and less than or equal to that of the fifth solar subcell, and having a band gap energy greater than that of the fourth solar subcell;
• wherein the fifth solar subcell has a band gap in the range of approximately 0.83 to 0.85 eV, the fourth solar subcell has a band gap of approximately 1.10 eV, the third solar subcell has a band gap in the range of 1.40 to 1.42 eV, the second solar subcell has a band gap of approximately 1.73 eV and the upper first solar subcell has a band gap of approximately 2.10 eV, and the first graded interlayer is compositionally graded to lattice match the third solar subcell on one side and the lower fourth solar subcell on the other side, and is composed of (InxGa1-x)yAl1-yAs with 0<x<1, 0<y<1, and x and y selected such that the band gap of the first graded interlayer is in a range of 1.42 to 1.60 eV throughout its thickness, and the second graded interlayer is compositionally graded to lattice match the fourth solar subcell on one side and the fifth solar subcell on the other side, and is composed of (InxGa1-x)yAl1-yAs with 0<x<1, 0<y<1, and x and y selected such that the band gap of the second graded interlayer is in a range of 1.20 to 1.40 eV throughout its thickness;
• and
• wherein the upper first solar subcell is composed of AlGaInP, the second solar subcell is composed of an InGaP emitter layer and an AlGaAs base layer, the third solar subcell is composed of GaAs or InxGa1-xAs (with 0<x<0.01), and the fourth solar subcell is composed of InGaAs, and the fifth solar subcell is composed of GaInAs.